During the operating life of a steam turbine, periodic maintenance, inspection and repair of steam turbine components must be performed. For example, certain portions of steam turbines, particularly those employed in nuclear power plants, must operate under a high pressure environment. The carbon steel material used for steam turbines, while meeting selected other engineering requirements, generally is not highly erosion resistant. Another factor is inlet steam flow conditions, which generally involve a high volume of steam near the saturation point. During operation under high pressure environments, the steam flow path through the turbine may cause unpredictable thermal hydraulic characteristics, such as high velocity turbulent conditions, which may result in an erosion-corrosion effect on these carbon steel parts. This erosion-corrosion reaction over time can tend to decrease the wall thickness of the pressure containing members and produce a rough surface. The rough surface, in turn, can accelerate the effect of the erosion-corrosion reaction, further increasing the turbulence within the steam flow path.
Normally, during periodic maintenance inspections, the steam turbine top cylinder half is unbolted and removed to conduct inspections. The top cylinder half is secured to the bottom cylinder half, at a mating area consisting of corresponding flange elements, by a plurality of bolts. After these bolts are removed, the steam turbine top cylinder half is lifted and removed from the bottom half. For inspection to be performed on the steam turbine top cylinder half, the cylinder half is typically suspended by means of a large overhead crane. Furthermore, work must be performed on the top cylinder half while it is suspended over head, or the cylinder half is rotated using cables and hooks suspended and operated by the overhead crane. In either case, the overhead crane is required, in which case it is unavailable for other plant operations.
An example of repair operations that may be performed on a steam turbine cylinder half are described in U.S. Pat. No. 5,049,716, which issued on Sep. 17, 1991, assigned to the present assignee and incorporated herein by reference, which is entitled "Steam Turbine Having Applied Novel Erosion-Resistant Surfaces and Methods for Applying These Surfaces". By way of brief explanation, erosion-resistant surfaces are welded to the steam turbine cylinder half to minimize the effects of the high velocity turbulent conditions. After the steam turbine cylinder half is removed, the carbon steel steam turbine component is cleaned prior to welding, by methods which are well known in the art. In order to more easily and quickly perform these operations, it would be advantageous to be able to perform them while the steam turbine cylinder half is inverted, or rotated to an upside down position. While rotating the top cylinder half can be accomplished by use of the overhead crane, such operations must necessarily be performed slowly, and can require large operating spaces within the turbine building. Moreover, special cribbing equipment is needed to hold the cylinder half in place while inspection and maintenance procedures are performed thereon. A typical procedure for inverting large steam turbine cylinder halves is discussed in U.S. Pat. No. 5,031,314, which issued on Jul. 16, 1991 to Berrong et al. This patent is assigned to the assignee hereunder, and is hereby incorporated by reference herein.
It is therefore desirable to provide a quicker method of inverting steam cylinder halves. Furthermore, by providing a separate apparatus for inverting the steam turbine cylinder halves, the plant's overhead crane is freed to be used for other maintenance procedures. Thus, other procedures can be performed in parallel with the work being done on the cylinder half, thus allowing maintenance procedures to be performed in less time.